1. Field of the Invention
The present invention relates to a terminal crimping structure and a terminal crimping method onto aluminum electric-wire, the terminal being used to be crimped onto the aluminum electric-wire and mounted within a connector housing, and relates to a producing method of an aluminum electric-wire with a terminal.
2. Description of the Related Art
There will be firstly described an object of the present invention. Conventionally, wire harnesses such as arranged within vehicular compartments have been typically made of copper electric-wires, and it has been rare to use aluminum electric-wires having deteriorated properties (physical properties) such as electric conductivity and strength. However, there have been recently increased such demands for using aluminum electric-wires, so as to reduce weights of vehicles and in view of recycling ability of the aluminum electric-wires. Meanwhile, electrical connectors have been typically used to connect wire harnesses to each other or to connect an in-vehicle equipment to a wire harness. Such electrical connectors are constituted of: connector housings to be fitted to each other; and multiple crimping terminals, to be inserted into and fitted to the connector housings, and crimpedly connected to electric-wires of wire harnesses; respectively.
Shapes of crimping portions of terminal metal-fittings constituting the crimping terminals include two types, opened barrel and closed barrel, and the former type is generally used from a standpoint of improved operability. Further, the compressed ratio (also called a surface-area reducing ratio, and hereinafter simply called “compressed ratio”) to be defined by a ratio of (cross-sectional area of electric-wire's conductor part at crimped portion)/(cross-sectional area of electric-wire's conductor part before crimping), is determined from such standpoints that the contact resistance is to be within a stability region, disconnection of electric-wire is not to be caused due to vibrations, and a sufficient fixing force to the electric-wire is to be achieved.
Note that compressed ratios of cross-sections of electric-wire's conductors upon crimping terminals are presently defined and controlled to be within a range of 75% to 95%, though such ratios are slightly changed depending on manufacturers, electric-wire sizes and the like (see Patent Document 1, for example).
Patent Document 1: Japanese Registered Utility Model No. 3005065 (pages 5-6, FIG. 6).
In conventional terminal crimping methods, terminals have been crimped onto copper electric-wire's conductor parts at the above-mentioned compressed ratios. Even when terminals are crimped onto copper electric-wires at such compressed ratios, the terminals are allowed to be connected to the copper electric-wires without any particular problems by virtue of the mechanical characteristics and electric characteristics of the copper electric-wires, so that the copper electric-wires connected with such terminals can be directly used without any inconvenience.
However, aluminum electric-wires have melting temperatures lower than those of copper electric-wires, and each of strands constituting an aluminum electric-wire is more apt to form an oxide film. Thus, electric current is flowed through limited strands to thereby easily cause a constriction resistance which in turn leads to a risk of: occurrence of melting; and defective conduction.
When aluminum electric-wires are actually crimped with terminals under the same conditions as copper electric-wires, resistances at terminal-crimped portions are increased due to environmental variations such as raised or lowered temperatures to thereby cause defects of conduction, thereby failing to maintain electric connecting states at satisfactory levels between terminals and electric-wires. As such, it is inappropriate to perform the crimping at the above-mentioned compressed ratios, insofar as concerned with a terminal crimping structure onto aluminum electric-wire.
There will be explained hereinafter another object of the present invention. In this explanation, there will be described a crimping process in a situation for crimping a terminal onto an aluminum electric-wire by way of experiment, based on a terminal crimping structure for copper electric-wire. FIG. 1 shows a conventional terminal to be crimped onto a copper electric-wire. As shown in FIG. 1, the terminal 580 is constituted of an inter-terminal connecting portion 580a and an electric-wire connecting portion 580b, and the electric-wire connecting portion 580b is constituted of: a pair of wire barrel pieces 581 each having a certain length in a terminal-wise longitudinal direction; and a pair of insulation barrel pieces 585 neighbored to the wire barrel pieces and crimped onto a coating part of the copper electric-wire. FIG. 2 is an explanatory view of a process for crimping such a terminal 580 onto an aluminum electric-wire 501 instead of a copper electric-wire. As apparent from this figure upon crimping the terminal, there is used a crimping jig 680 provided with terminal crimping portions 681, 685 corresponding to the wire barrel pieces 581 and insulation barrel pieces 585 of the terminal 580, respectively. Note that, when viewed in a longitudinal direction of a terminal to be crimped, the crimping jig 680 is formed with crimping grooves each having an inverted “V” shape as a whole and having an “M” shape at an apex of the inverted “V” shape for curling the tip ends of the barrel pieces in the caulking direction. Further, such a crimping jig 680 is downwardly moved from the above of the terminal 580 (see an arrow X showing a terminal crimping direction in the figure), thereby deforming the barrel pieces 581, 585 of the terminal 580 along the groove surfaces in the inverted “V” shapes of the jig 680 (see FIG. 2B and FIG. 2C). Since each groove surface in the inverted “V” shapes of the jig 680 has its tip end in the “M” shape, further urging the jig 680 toward the terminal 580 causes the end portions of the barrel pieces 581, 585 to be curled toward the aluminum electric-wire 501 in the direction for caulking the barrel tip ends, respectively. This crimps the barrel pieces 581, 585 onto an electrical conductor part 501a and a coating part 501b of the aluminum electric-wire 501 (see FIG. 2C and FIG. 3A), respectively. When the terminal 580 is firmly crimped onto the aluminum electric-wire 501, the crimping jig 680 is raised in a Y direction in the figure, thereby completing the terminal crimping process.
Note that those terminals are also known which have such structures each including a wire barrel which is not constituted of a pair of barrel pieces as in the terminal 580 but constituted of multiple pairs of barrel pieces (see Patent Document 2 through Patent Document 4).
Patent Document 2: JP-U-6-36215 (pages 4-5, FIG. 2)
Patent Document 3: JP-U-6-36216 (pages 4-5, FIG. 2)
Patent Document 4: JP-A-11-297375 (pages 3-4, FIG. 1)
Next, there will be explained a further object of the present invention.
In the method for connecting copper electric-wires and terminals to each other, although the terminal 580 is not contacted with all of the strands constituting the copper electric-wire, the terminal has been allowed to be connected to the copper electric-wire without any particular problems by virtue of the mechanical characteristics and electric characteristic of the copper electric-wire.
However, aluminum electric-wires have weaker mechanical strengths and lower melting temperatures as compared with copper electric-wires, and have such properties that each of the strands constituting the aluminum electric-wire is apt to form an oxide film. Thus, electric current is flowed through limited strands to thereby easily cause a constriction resistance which in turn leads to a risk of: occurrence of melting; and defective conduction.
Concretely, when the terminal is strongly crimped onto an aluminum electric-wire to such an extent that oxide films of strands are broken and the strands themselves and the strands and wire barrel pieces are extremely closely contacted with each other, the crimped structure is allowed to withstand an environmental test such as thermal cycles insofar as concerned with an electric conducting property. However, the electric-wire retaining force is extremely deteriorated due to the excessive stress affecting the terminal-crimped portion, thereby possibly resulting in an inappropriate connecting structure when used between a terminal and an electric-wire.
FIG. 3 shows a state where the terminal 580 is crimped onto such an aluminum electric-wire 501, by a plan view (FIG. 3A) and a side view (FIGS. 3B, C). Note that, when viewed in a terminal crimping direction in FIG. 3B, the crimped portions of the wire barrel pieces 581 have the same heights as those in the crimping of a conventional copper electric-wire, relative to the electrical conductor part 501a of the aluminum electric-wire 501 (see height He in the drawing). Further, FIG. 3C shows a state where the terminal 580 is crimped at a compressed ratio (surface-area reducing ratio) higher than that in FIG. 3B so that the terminal 580 has a height (see height Hf in the drawing) lower than FIG. 3B when viewed in a terminal crimping direction.
In the crimped state shown in FIG. 3B which is the same as the conventional copper electric-wire, although the terminal crimping strength (electric-wire retaining force) is not problematic, oxide films on the surfaces of the strands of the electrical conductor part 501a are not sufficiently broken, and there is caused an increased contact resistance in an environmental test such as thermal cycles, thereby resulting in an insufficient electric conducting property. Meanwhile, when the terminal 580 is crimped onto the aluminum electric-wire 501 at a higher compressed ratio (surface-area reducing ratio) as shown in FIG. 3C, electric conduction is certainly and sufficiently achieved, but the electric-wire retaining force is deteriorated due to the increased stress affecting the terminal-crimped portion of the electric-wire, thereby failing to obtain a terminal crimping strength required for each electric-wire size.
Note that each of the terminals described in the Patent Document 2 through Patent Document 4 has a constitution formed with multiple pairs of wire barrel pieces in addition to a pair of insulation barrel pieces. However, the pairs of wire barrel pieces are individually formed so as to correspond to different diameters of crimping-targeted electric-wires, respectively, and there is never disclosed such a constitution to crimp a terminal onto an electrical conductor part of an aluminum electric-wire having a certain diameter, simultaneously at different compressed ratios (surface-area reducing ratios) by the pairs of wire barrel pieces, respectively.